Freymann, G. von

Hermatschweiler, M.

Thiel, M.

Wegener, M.

English

KITopen

Thin-film polarizer based on a one-dimensional–three-dimensional–one-dimensional photonic crystal heterostructureM. Thiel,a M. Hermatschweiler, and M. WegenerInstitut für Angewandte Physik, Universität Karlsruhe (TH), Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe,Germany and DFG-Center for Functional Nanostructures (CFN), Universität Karlsruhe (TH),Wolfgang-Gaede-Straße 1, D-76131 Karlsruhe, GermanyG. von FreymannInstitut für Nanotechnologie, Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft,D-76021 Karlsruhe, GermanyReceived 15 June 2007; accepted 31 August 2007; published online 20 September 2007The recent experimental demonstration of polarization stop bands in three-dimensional dielectriccircular-spiral photonic crystals is extended in two ways. First, the combination with aone-dimensional set of lamellae on one side allows for “poor-man’s optical isolators” or forthin-film polarizers—depending on from which side light impinges onto the device. Second, a chiralthree-dimensional photonic crystal sandwiched between two one-dimensional sets of lamellae actsas a thin-film polarizer from both sides. Corresponding polymeric heterostructures are fabricated bymeans of direct laser writing. Their performance is compared with theory. © 2007 AmericanInstitute of Physics. DOI: 10.1063/1.2789662Chiral molecules can exhibit circular dichroism and/oroptical activity—despite the fact that the molecular dimen-sions are typically several orders of magnitude smaller thanthe pitch of the spiral described by the tip of the field vectorof circularly polarized light i.e., the wavelength of light. Inchiral photonic crystals, e.g., in circular-spiral structures, thetwo spiral pitches can be brought into resonance and polar-ization stop bands emerge.1,2 In a polarization stop band, oneincident circular polarization of light is transmitted withnegligible polarization conversion whereas the other circu-lar polarization is Bragg reflected.1,2 Clearly, the suppressioncan be adjusted by the number of lattice constants along thepropagation direction, but even less than ten lattice constantsand low index contrast can lead to very large effects forappropriate design. Our recent corresponding experimentaldemonstration based on polymeric three-dimensionalcircular-spiral photonic crystals allows for normal incidenceonto “thin-film” structures located on a substrate.2 Relatedchiral structures have, however, also been discussed forwaveguide geometries,3 for optical fibers,4 for photonic bandgap materials,5–7 for chiral sculptured thin films,8,9 for layer-by-layer chiral photonic crystals,10,11 as well as in the contextof cholesteric liquid crystals.12Polarization stop bands can be used as “poor-man’s op-tical isolators” for circularly polarized incident light: If, forexample, right-handed polarized light from a laser impingesonto the structure, it is transmitted for a spiral photonic crys-tal composed of left-handed dielectric spirals. Upon backreflection from a mirror behind the spiral photonic crystal,the backward propagating light has left-handed circular po-larization. As the spirals keep their handedness when lookedat from the other side, the light is not transmitted, hence,blocked from propagating back into the laser source. Thisdevice is only a “poor-man’s” isolator because it will fail toisolate if the polarization state of light is messed up behindthe device, which is in sharp contrast to true optical isolatorsbased on the Faraday effect.Furthermore, a polarization stop band obviously con-verts unpolarized incident light into circularly polarizedtransmitted light, which in itself might be of interest for cer-tain applications. Moreover, the combination of a chiral pho-tonic crystal and a quarter-wave plate clearly acts as a polar-izer. In contrast with commercially available thin-filmpolarizers based on one-dimensional dielectric stacks andBrewster’s angle,13 such heterostructure can work for normalincidence of light. If the device is used in the opposite direc-tion, i.e., if linearly polarized incident light oriented 45°with respect to the principal axes of the quarter-wave platefirst hits the quarter-wave plate and then the chiral photoniccrystal, the overall structure acts as a poor-man’s optical iso-lator for linear incident polarization of light. A chiral photo-nic crystal sandwiched between two crossed quarter-waveplates can act as a polarizer from both sides.To obtain compact and monolithic devices, it is desirableto integrate the chiral photonic crystal and one or twoquarter-wave plates. It is the aim of the present paper todemonstrate such heterostructures.The physics as well as the fabrication of the three-dimensional 3D circular-spiral photonic crystals have beendescribed previously.1,2 The quarter-wave plates are simplyone-dimensional 1D periodic sets of lamellae, leading toform birefringence in the long-wavelength limit. The latticeconstants of the 3D and the 1D structures, respectively, donot need to be identical but choosing the same lattice con-stant is possible and eases the theoretical calculations, hencethe detailed design. Figure 1 shows the two types of hetero-structures discussed above. In what follows, we emphasizethe 1D-3D-1D heterostructure, the 1D-3D heterostructureyields very similar spectra. Parameters are a=1.3 m,c=1.3 m, d=0.78 m, h=3.7 m, 2rx=0.44 m, andN=6. The volume filling fraction of the spirals in the cubicunit cell is 32.1%. These parameters result from an optimi-zation acknowledging the fabrication restrictions of directaElectronic mail: michael.thiel@physik.uni-karlsruhe.deAPPLIED PHYSICS LETTERS 91, 123515 20070003-6951/2007/9112/123515/3/$23.00 © 2007 American Institute of Physics91, 123515-1Downloaded 20 Mar 2009 to 129.13.72.198. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jspFirst published in:EVA-STAR (Elektronisches Volltextarchiv – Scientific Articles Repository) http://digbib.ubka.uni-karlsruhe.de/volltexte/1000010997laser writing see below. The thickness of each of the twoplates introduced for mechanical stability between the spi-ral crystal and the sets of lamellae is 0.93 m. The complete1D-3D-1D heterostructure has a height of only 17 m.The calculated optical response obtained from ascattering-matrix approach14,15 of a 1D-3D-1D heterostruc-ture is shown in Fig. 2. This calculation refers to normalincidence onto the structure depicted in Fig. 1 and assumes arefractive index n=1.57 for the polymer. The structure islocated on a glass substrate with refractive index n=1.518.Linear optical intensity transmittance spectra are shown forthe two incident linear polarizations including +45° and−45° with respect to the lamellae, respectively. Here, +45°leads to left-handed circular polarization, while −45° toright-handed circular polarization. Obviously, the transmit-tances are different by about a factor of 50. The polarizationstate emerging from the device is very close to linear andparallel to the incident linear polarization. This becomes evi-dent from the top part of Fig. 2 where we analyze the emerg-ing polarization state at the operation wavelength see dot.The performance of the 1D-3D heterostructure is quite simi-lar, except that circular polarization is emerging from thedevice not shown.As pointed out above, the 1D-3D-1D heterostructure actsas a polarizer. Furthermore, it also acts as an optical diode inthe following sense: Light impinging with a linear polariza-tion oriented at −45° with respect to the lamellae is transmit-ted for the geometry discussed above. If we now turn aroundthe device by 180° such that the new incident linear polar-ization corresponds to +45° with respect to the lamellae onthe new front side, the light is not transmitted. Unfortunately,this behavior is not equivalent to that of an optical isolator.This would require that light transmitted by the device andback reflected from a mirror behind the device would notpropagate back into the laser source.To validate our discussion, we have fabricated the1D-3D as well as the 1D-3D-1D structure shown in Fig. 1by standard two-photon direct-laser-writing into the com-mercially available thick-film photoresist SU-8.16–19 Thefollowing discussion again focuses on the more complex1D-3D-1D case, electron micrographs of which are shown inFig. 3. Optical characterization for incident linearly polarizedlight is shown in Fig. 4. For linear incident polarization ori-ented at +45° with respect to the lamellae, a transmittanceclose to 78% is observed at 1.72 m wavelength, whereasthe transmittance is around 1.5% for −45° polarization. Thus,FIG. 1. Color online Proposed 1D-3D blue and 1D-3D-1D blue andgreen photonic crystal heterostructure composed of a three-dimensionalright-handed RH spiral photonic crystal with N=6 pitches and one or twoone-dimensional sets of lamellae, respectively. Parameters are defined on theright-hand side.FIG. 2. Calculated normal-incidence transmittance spectra logarithmicscale of the 1D-3D-1D heterostructure Fig. 1. The linear incident polar-ization is oriented = +45° solid and =−45° dashed with respect to thelamellae, respectively see inset. Pronounced differences occur in theregion of the polarization stop band gray area. The corresponding trans-mittance ratio at 1.72 m wavelength is about 50. The emerging polariza-tion of light at this wavelength is analyzed in the upper part.FIG. 3. Electron micrographs of the fabricated heterostructure: a glancing-angle incidence view and b oblique-view image. The inset shows anormal-incidence close-up view onto the top set of lamellae. c close up ofa revealing parts of the 3D spiral crystal RH, one of the stabilizing plates,the bottom lamellae, and the surrounding wall with one of the drains leftbottom allowing for developer circulation.123515-2 Thiel et al. Appl. Phys. Lett. 91, 123515 2007Downloaded 20 Mar 2009 to 129.13.72.198. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jspthe suppression factor is 52 17.2 dB. Furthermore, thepolarization state of the light emerging from our thin-filmoptical isolator is very close to linear as determined byrotating a Glan-Thomson polarizer behind the sample seeinset of Fig. 4. The fit solid to the data reveals a depen-dence of the transmittance T according to T=0.044+0.683 cos2, where  is the analyzer angle. The overallmeasured behavior Fig. 4 is in very good agreement withthe numerically calculated response Fig. 2. In particular,the spectral position as well as the depth of the polarizationstop bands gray area in Figs. 2 and 4 agree well. Regardingthe deviations with respect to the spectral shape, one shouldbe aware that the experiment introduces a certain angle av-eraging via the finite opening angle of the incident light 5°.In contrast, the theory refers to strictly normal incidence. Wehave previously shown that this effect slightly reshapes thespectra.2 Deviations from perfect linear polarization of theemerging light are likely due to sample imperfections. Nev-ertheless, we can conclude that the quality of the fabricatedstructure is very high and that the concept is valid.In conclusion, we have proposed, fabricated, and char-acterized photonic heterostructures composed of chiral three-dimensional spiral photonic crystals and one-dimensionalsets of lamellae acting as quarter-wave plates. These hetero-structures can serve as thin-film polarizers, poor-man’s opti-cal isolators, and as optical diodes in the sense definedabove.We thank R. Baets for clarifying discussions regardingoptical isolators. We acknowledge support by the DeutscheForschungsgemeinschaft DFG and the State of Baden-Württemberg through the DFG-Center for Functional Nano-structures CFN within subproject A1.4. The research ofG.v.F. is further supported through a DFG Emmy Noetherfellowship DFG-Fr 1671/4-3. The PhD education of M.T.and M.H. is further supported by the Karlsruhe School ofOptics and Photonics KSOP.1J. Lee and C. Chan, Opt. Express 13, 8083 2005.2M. Thiel, M. Decker, M. Deubel, M. Wegener, S. Linden, and G. vonFreymann, Adv. Mater. Weinheim, Ger. 19, 207 2007.3G. Shvets, Appl. Phys. Lett. 89, 141127 2006.4V. I. Kopp, V. M. Churikov, J. Singer, N. Chao, D. Neugroschl, and A. Z.Genack, Science 305, 74 2004.5A. Chutinan and S. Noda, Phys. Rev. B 57, R2006 1998.6O. Toader and S. John, Science 292, 1133 2001.7K. Busch, G. von Freymann, S. Linden, S. F. Mingaleev, L.Tkeshelashvili, and M. Wegener, Phys. Rep. 444, 101 2007.8K. Robbie, M. J. Brett, and A. Lakhtakia, Nature London 384, 6161996.9P. C. P. Hrudey, B. Szeto, and M. J. Brett, Appl. Phys. Lett. 88, 2511062006.10J. C. W. Lee and C. T. Chan, Appl. Phys. Lett. 90, 051912 2007.11M. Thiel, G. von Freymann, and M. Wegener, Opt. Lett. 32, 2547 2007.12J. Hwang, M. H. Song, B. Park, S. Nishimura, T. Toyooka, J. W. Wu, Y.Takanishi, K. Ishikawa, and H. Takezoe, Nat. Mater. 4, 383 2005.13L. Li and J. A. Dobrowolski, Appl. Opt. 35, 2221 1996.14D. M. Whittaker and I. S. Culshaw, Phys. Rev. B 60, 2610 1999.15S. G. Tikhodeev, A. L. Yablonskii, E. A. Muljarov, N. A. Gippius, and T.Ishihara, Phys. Rev. B 66, 045102 2002.16S. Kawata, H.-B. Sun, T. Tanaka, and K. Takada, Nature London 412,697 2001.17M. Deubel, G. von Freymann, M. Wegener, S. Pereira, K. Busch, and C.M. Soukoulis, Nat. Mater. 3, 444 2004.18K. K. Seet, V. Mizeikis, S. Matsuo, S. Juodkazis, and H. Misawa, Adv.Mater. Weinheim, Ger. 17, 541 2005.19A. Ledermann, L. Cademartiri, M. Hermatschweiler, C. Toninelli, G. A.Ozin, D. S. Wiersma, M. Wegener, and G. von Freymann, Nat. Mater. 5,942 2006.FIG. 4. Measured transmittance spectra. Experimental data obtained fromthe structure shown in Fig. 3, represented in the same format as in Fig. 2theory.123515-3 Thiel et al. Appl. Phys. Lett. 91, 123515 2007Downloaded 20 Mar 2009 to 129.13.72.198. Redistribution subject to AIP license or copyright; see http://apl.aip.org/apl/copyright.jsp

Thin-film polarizer based on a one-dimensional-three-dimensional-one-dimensional photonic crystal heterostructure

https://publikationen.bibliothek.kit.edu/1000010997/755743

Thin-film polarizer based on a one-dimensional-three-dimensional-one-dimensional photonic crystal heterostructure

Abstract

Similar works

Full text

Available Versions

KITopen